1. Field of the Invention
The present invention relates to a data broadcast system and method and, more particularly, to a method of broadcasting data services with broadcast signals and a system for selectively providing portions of the broadcast data service to the user.
2. Description of the Related Art
Digital television systems have become widely used for broadcast systems. The digital television systems provide digitisation and compression of the image to be broadcast with technologies such as MPEG-2 compression. The broadcast pictures are hence encoded and conveyed to the digital television receivers in the home as a digital data sequence. Digital television has a number of advantages over conventional analogue television, such as increased capacity and increased robustness to noise and interference.
Digital television systems also allow many kinds of data to be carried seamlessly within broadcasts carrying audio and visual data. Hence, many new services can be provided through the digital TV receiver to the viewer.
A popular analogue service that uses additional data carried within the broadcast transmission is the teletext service. The teletext service is carried as digital data within certain transmission lines of the vertical blanking interval (VBI) of the TV signal. The VBI is the time allowed for the raster scan to return to the top of the screen and hence this time is not used to carry any useful picture information. Some lines are set aside for teletext data and the digital data is modulated onto the broadcast TV signal.
Teletext systems broadcast a number of “pages” of data in cycles with a page being typically updated every 2 to 3 minutes. The update cycle time depends on how many pages are broadcast in the cycle, there being only a small bandwidth available for the teletext data. Upon selecting a page, the viewer has to then wait for the page to be delivered as part of the cycle—this time will be on average half the total cycle time for all the pages.
Typical teletext systems provide the latest news, sport and TV guide information and also reference information and advertising. Teletext systems are very useful for providing “headline” information such as sports results when there is no other means of obtaining the information.
A very popular use for the teletext systems is to find out the latest information for some rapidly changing event such as a sports event. Often this can be the only way the viewer can obtain this information, because sports events are often not screened live, are carried as part of a pay-per-view service or have finished such that the programmes are now carrying other content. Hence, this allows the viewer to catch up with “missed” content such as sports events or news broadcasts by other means using the data services.
A problem with previous broadcast data services is that they communicate very little information—perhaps just the score of a football match for instance. The user, although not wanting to see the whole sports event, would like a little more information than just the score—maybe to see video of the goals or near misses in the example of a football match.
However, to provide a service like this there are further problems. Simple data services such as teletext can be provided easily with a low bandwidth. Providing an enhanced data service with audio and visual data would require more bandwidth or take a lot longer to update and cycle the information.
Viewers have different interests and priorities, so what is important to one viewer is of little interest to another. Screening news “highlights” in a sequence that repeats and updates every 15 minutes is not appealing to a viewer if they have one item they would like to see and have to wait an average of 7.5 minutes to see this item.
Digital broadcast systems can provide more bandwidth for program content. However, this bandwidth is still at a premium. Using some of the bandwidth to provide broadcast data services can be considered wasteful, particularly if there is other content that could be screened at the same time to a reasonable audience. Indeed, screening live video and audio as a broadcast data service will still take up approximately 2 Mbit/s of bandwidth using MPEG-2 compression.